Postage meters are well known and manufacturers are continuously attempting to design meters which combine the desirable attributes of simplicity of use, small size, lightness, low manufacturing cost and reliable, trouble-free operation. A prior art postage meter is shown in U.S. Pat. No. 2 510 350.
The present invention is intended for incorporation in postage meters such as are described, illustrated and claimed in our co-pending patent applications as follows:
U.K. application Ser. No. 2 180 193 published 25th March 1987, European application Ser. No. 222946 published 27th May 1987 and European application No. 86 302 035.0 filed 19th March 1986, and U.S. application Ser. No. 089,640 filed on Aug. 26, 1987. The contents of these applications are hereby incorporated into the present application to the extent necessary for a full understanding of the present invention, in order to avoid redundant repetition.
In some prior known designs of postage meter (see for example British Patent No. 2 056 610) a particular kind of drive coupling (also called a clutch) is included. The Patentees state:
"With franking machines, a transport or conveying mechanism usually serves both to feed in and press the item to be stamped against a printing drum. Such a transport mechanism needs to be synchronised with the printing control drum of the franking machine in such a way that an exact feeding and conveying of the item is guaranteed during the franking process".
In a certain prior mechanism of this kind, at the end of a single revolution of the print drum, an inner shaft of the drive shaft continues rotating so as to provide drive to an envelope ejection roller. The drive coupling (clutch) ensured that no further rotation of the output shaft from the clutch and hence of the print drum could take place. Because of the single-revolution clutch, the mechanism could not be re-energised for a further single revolution until one revolution has been completed and this revolution would ensure that the envelope had been successfully ejected and the mechanism reset for a fresh franking operation.